ABSTRACT
Chapter 6dealtwithxedschedules, inwhichdeparturetimescouldnotbechanged. In practicaltransitscheduling, however, schedulersshouldattempttoallocatevehiclesinthemost efcientmannerpossible, includingtheemploymentofsmallshiftsindeparturetimes. For example, in Egged, Israel’s national bus carrier, the schedulers consider a variable instead of a xed schedule in addition to DH trip insertions. That is, they mull shifting trip-departure times (SDTs), basedonsomeacceptabletolerances. Althoughcondentoftheir work efciency, the
Egged schedulers agree that variable scheduling with DH trip insertions is a very complex process, notsystematic, andaverytime-consumingtask;itcanturnagoodscheduleintoa souredone. This situationisanaloguetothefollowingtruth. Ifyouputaspoonfulofwine (anefcientchainoftrips)intoabarrelofsewage(problematicschedule), yougetsewage. If you putaspoonfulofsewage(achainoftripsimpossibletoexecute)inabarrelfullofwine (implemental schedules), you still get sewage (problematic schedule).
